The present invention relates to a reference voltage generating circuit and, more particularly, to a bandgap reference voltage generating circuit using an operational amplifier.
As already known, a bandgap voltage generating circuit is used as a reference power source of, for example, a three-terminal IC regulator made up of bipolar transistors (R. J. Widlar, "New Developments in IC Voltage Regulators", IEEE Journal of Solid-State Circuits, Vol. SC-6, pp. 2-7, (1971)). The bandgap reference voltage generating circuit is indispensable to an electronic circuit which requires a reference voltage of a high stability and precision against any variations or changes such as in power supply voltage or in temperature. With the recent advancement in analog MOS techniques, the bandgap reference voltage generating circuit is now used also in MOS integrated circuits such as for analog-to-digital converters. Since a bipolar transistor having good properties can hardly be obtained by a process ordinarily employed for the manufacture of CMOS integrated circuits, the circuit generally used is one as shown in FIG. 5 (K. E. Kujik, "A Precision Reference Voltage Source", IEEE Journal of Solid-State Circuits, Vol. SC-8, pp. 222-226, (1973)). This circuit configuration does not require bipolar transistors and comprises diodes, resistors and an operational amplifier, so that a bandgap reference voltage generating circuit can easily be formed by a process for the manufacture of CMOS semiconductor integrated circuits.
However, the above conventional circuit requires a start-up resistor having a large resistance value and this results in an increase in a chip size. Also, the increase in the power supply voltage causes an increase in the current flowing in the start-up resistor, so that the output voltage necessarily has a dependency on the power supply voltage.